No weight loss

I don't know if you are a man or a woman, but your cycle will affect how much water you retain, and that might be skewing the numbers. I know the week before my time, I don't appear to be loosing weight, but then a week or so later, I will drop several pounds all at once.

Other possible reasons:

exercising and muscle building all contribute to bigger, heavier muscles, so even if you loose fat, you gain muscle and the scale doesn't seem to change. Measuring inches lost might be a better gauge.

You may not be recording your cal intakes correctly. Are you logging liquid calories? logging the little nibble here and there? I have a very bad habit of finishing off my kids last few bites, and tasting my husband's selections at the restaurant. I record it even if it's a nibble. It's amazing how those nibbles add up.

Also, how are you measuring your food? if you are not used to weighing food, you may not know how big 3 oz or 100 g really is. Perhaps your idea of a "serving" is bigger than the serving size listed in MFP.

You said you don't eat back the cals you burn off in exercise. That's fine, I don't either, usually, unless my net total for the day is under 1000 because I exercised so awesomely. if so, i try to eat back until 1200. You should be eating at least 1200 a day, or your body will think there is a famine and it hill hold on to it's fat reserves dearly. That's why MFP calculates your net calories in addition to your food calories.

Finally, it's possible that your body got used to a calorie restricted diet while on WW and has adjusted itself to function according to that restriction. In that case, 1500 cals is "maintenance mode" for your body, not diet mode. If you are 200+ though, i doubt this is the issue.